The disclosure of Japanese patent application no.2002-167749 filed on Jun. 7, 2002 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an evaporative fuel processing apparatus. More particularly, the invention relates to an evaporative fuel processing apparatus suitable for processing evaporative fuel generated in an internal combustion engine without releasing the evaporative fuel into the atmosphere, and a control method of the same.
2. Description of the Related Art
As art related to the invention, for example, as disclosed in Japanese Patent Laid-Open Publication No. 7-91330, an evaporative fuel processing apparatus is known in which evaporative fuel generated in a fuel tank is stored in a canister so as to be processed. The evaporative fuel processing apparatus is for preventing the evaporative fuel from being released into the atmosphere. Accordingly, the evaporative fuel processing apparatus needs to have a function of promptly detecting leakage which has occurred therein.
The apparatus according to the related art has a function of applying pressure to a system including the fuel tank and the canister using a booster pump after closing the system. There is a difference in changes in pressure in the system after the application of pressure between when leakage has occurred in the system, and when leakage has not occurred in the system. Accordingly, the apparatus determines the presence or absence of leakage based on a change in the pressure in the system after the application of pressure.
When leakage has occurred in the evaporative fuel processing apparatus, it is preferable that the location of leakage can be determined. However, the apparatus cannot determine the location of leakage in the system including the fuel tank and the canister.
Also, in the evaporative fuel processing apparatus, it is necessary to isolate the fuel tank from the atmosphere in order to prevent the evaporative fuel that is generated while an internal combustion engine is stopped from being released into the atmosphere. According to the apparatus, it is possible to satisfy this requirement by maintaining the entire system including the fuel tank and the canister in a closed state.
However, an internal pressure in the system may become high due to generation of the evaporative fuel. Accordingly, it is necessary to make the structure of the entire system including the fuel tank and the canister pressure-resistant in order to close the system so as to prevent the evaporative fuel from being released into the atmosphere. Therefore, it is difficult to realize the apparatus at a low cost and in a light weight.
The invention is made in order to solve the above-mentioned problem. Accordingly, it is an object of the invention to provide an evaporative fuel processing apparatus and control method of the same, in which a state where a fuel tank and a canister are isolated from each other can be realized.
An evaporative fuel processing apparatus according to a first aspect of the invention includes a fuel tank; a canister which communicates with the fuel tank through a vapor passage; a purge passage which permits communication between an intake passage of an internal combustion engine and the canister; an open/close valve which opens or closes the vapor passage; an isolated state switching mechanism which makes the canister open to the atmosphere or which isolates the canister from the atmosphere; a pressure adjusting mechanism which increases or reduces the pressure in the canister; a purge control valve which opens or closes the purge passage; and a control system which controls the open/close valve, the isolated state switching mechanism, the pressure adjusting mechanism and the purge control valve.
According to the first aspect of the invention, in addition to the fact that it is possible to realize the basic functions (storage/purge of the evaporative fuel, and a leakage diagnosis) as the evaporative fuel processing apparatus, it is possible to allow the canister and the fuel tank to form a single space or separate spaces by opening or closing the open/close valve.
In a second aspect of the invention, the control system according to the first aspect may further closes a canister space which includes the canister and which does not include the fuel tank by closing the open/close valve, isolating the canister from the atmosphere using the isolated state switching mechanism, and closing the purge control valve, adjusts an internal pressure in the closed canister space using the pressure adjusting mechanism, and performs a diagnosis on leakage (hereinafter, referred to as a xe2x80x9cleakage diagnosisxe2x80x9d) in the canister space based on the adjusted internal pressure in the canister space.
According to the second aspect of the invention, it is possible to perform a leakage diagnosis for the canister space while the fuel tank is isolated from the canister. Therefore, it is possible to detect leakage only for the canister space.
In a third aspect of the invention, the control system according to the second aspect may further prohibits the opening of the open/close valve when it is determined that leakage has occurred in the canister space.
According to the third aspect of the invention, when there is leakage in the canister space, it is possible to prohibit the opening of the open/close valve and prevent leakage of the evaporative fuel from the leakage portion.
In a fourth aspect, the control system according to either the second or third aspect may further closes an entire space including the canister and the fuel tank as a single space by opening the open/close valve, isolating the canister from the atmosphere using the isolated state switching mechanism, and closing the purge control valve when it is determined that leakage has not occurred in the canister space, adjusts the internal pressure in the closed entire space using the pressure adjusting mechanism, and performs a leakage diagnosis for the entire space based on the adjusted internal pressure in the entire space.
According to the fourth aspect of the invention, when it is determined that there is no leakage in the canister space, it is possible to determine whether there is leakage in the entire space including the fuel tank. In this case, when there is leakage on the fuel tank side, it is possible to detect leakage as an abnormality on the fuel tank side.
In a fifth aspect of the invention, the control system according to the second aspect may further close an entire space including the canister and the fuel tank as a single space by opening the open/close valve, isolating the canister from the atmosphere using the isolated state switching mechanism, and closing the purge control valve after the completion of the leakage diagnosis for the canister space, adjusts the internal pressure in the closed entire space using the pressure adjusting mechanism, performs a leakage diagnosis for the entire space based on the adjusted internal pressure in the entire space.
According to the fifth aspect of the invention, it is possible to determine whether leakage has occurred in the entire space including the fuel tank regardless of whether leakage has occurred in the canister space. According to the results of the two diagnoses performed in the fifth aspect of the invention, it is possible to detect leakage in the apparatus and specify the location of the leakage.